BaseService terminology: Rename url to route (#2278)

The term “url” is overloaded in services, to refer to the Shields route and also the API URL. Calling the Shields URL a “route” is on the whole more descriptive, and makes it clearer and more obvious which one of these we’re talking about. It’s a small thing, though seems like an improvement.

We have a few functions called `buildUrl`. I’ve renamed them to `buildRoute` when they refer to routes, and left them as `buildUrl` when they refer to API URLs.

I included a minor style tweak and some formatting cleanup in `TUTORIAL.md`.

services/sourcegraph/sourcegraph.service.js

@@ -8,7 +8,7 @@ module.exports = class Sourcegraph extends LegacyService {
     return 'other'
   }
 
-  static get url() {
+  static get route() {
     return {
       base: 'sourcegraph/rrc',
     }